It is the goal of these interdisciplinary studies to elucidate the molecular mechanisms of auditory processing at the hair cell. A major emphasis is directed towards those mechanisms that regulate and modulate the transduction process. The projects combine biochemical, pharmacological, electrophysiological and anatomical techniques and will test hypotheses pertaining to the regulation of neurotransmission and mechanisms of efferent action. The mammalian (guinea pig) inner ear will be investigated in all studies and specific questions additionally will be addressed in simpler systems such as the Xenopus lateral line and the isolated outer hair cell. The work is based on current hypotheses of cell function, on previous results from the participating laboratories, and state-of-the-art methodology. The studies begin with the hypothesis that neurotransmission at the hair-cell, afferent nerve synapse is biochemically regulated both pre- and post-synaptically. We will test which mechanisms regulate neurotransmitter release from the Xenopus lateral line and characterize glutamate receptors and their actions in the mammalian cochlea. The second hypothesis is that efferent transmitters regulate afferent mechanisms. We will immunocytochemically determine the presence of GABA and acetylcholine receptors and test whether efferent transmitters modulate the release of the afferent transmitter and whether they control voltage- dependent membrane conductances. Thirdly, we will test the hypothesis that the efferent transmitter(s) modulate the active biomechanical mechanism ("slow" motility) of outer hair cells via second messenger systems and the control of intracellular calcium. We will investigate whether cholinergic receptors mediate efferent action on outer hair cell potentials and calcium channels, and on intracellular calcium and motility. Finally, we will test the hypothesis that these efferent actions on motility and calcium require a G- protein/phosphoinositide second messenger system that regulates intracellular inositol phosphates and protein phosphorylation. These studies are integrated with other projects of this grant, particularly those in the anatomical and physiological sections. The results will expand our knowledge of basic molecular mechanisms in auditory transduction and will provide a basis for future investigations of cochlear dysfunctions underlying hearing disorders.